#include "cache.h"
#include <sys/wait.h>

static const char receive_pack_usage[] = "git-receive-pack [--unpack=executable] <git-dir> [heads]";

static const char *unpacker = "git-unpack-objects";

static int path_match(const char *path, int nr, char **match)
{
        int i;
        int pathlen = strlen(path);

        for (i = 0; i < nr; i++) {
                char *s = match[i];
                int len = strlen(s);

                if (!len || len > pathlen)
                        continue;
                if (memcmp(path + pathlen - len, s, len))
                        continue;
                if (pathlen > len && path[pathlen - len - 1] != '/')
                        continue;
                *s = 0;
                return 1;
        }
        return 0;
}

static void safe_write(int fd, const void *buf, unsigned n)
{
        while (n) {
                int ret = write(fd, buf, n);
                if (ret > 0) {
                        buf += ret;
                        n -= ret;
                        continue;
                }
                if (!ret)
                        die("write error (disk full?)");
                if (errno == EAGAIN || errno == EINTR)
                        continue;
                die("write error (%s)", strerror(errno));
        }
}

/*
 * If we buffered things up above (we don't, but we should),
 * we'd flush it here
 */
static void flush_safe(int fd)
{
}

/*
 * Write a packetized stream, where each line is preceded by
 * its length (including the header) as a 4-byte hex number.
 * A length of 'zero' means end of stream (and a length of 1-3
 * would be an error). 
 */
#define hex(a) (hexchar[(a) & 15])
static void packet_write(const char *fmt, ...)
{
        static char buffer[1000];
        static char hexchar[] = "0123456789abcdef";
        va_list args;
        unsigned n;

        va_start(args, fmt);
        n = vsnprintf(buffer + 4, sizeof(buffer) - 4, fmt, args);
        va_end(args);
        if (n >= sizeof(buffer)-4)
                die("protocol error: impossibly long line");
        n += 4;
        buffer[0] = hex(n >> 12);
        buffer[1] = hex(n >> 8);
        buffer[2] = hex(n >> 4);
        buffer[3] = hex(n);
        safe_write(1, buffer, n);
}

static void show_ref(const char *path, unsigned char *sha1)
{
        packet_write("%s %s\n", sha1_to_hex(sha1), path);
}

static int read_ref(const char *path, unsigned char *sha1)
{
        int ret = -1;
        int fd = open(path, O_RDONLY);

        if (fd >= 0) {
                char buffer[60];
                if (read(fd, buffer, sizeof(buffer)) >= 40)
                        ret = get_sha1_hex(buffer, sha1);
                close(fd);
        }
        return ret;
}

static void write_head_info(const char *base, int nr, char **match)
{
        DIR *dir = opendir(base);

        if (dir) {
                struct dirent *de;
                int baselen = strlen(base);
                char *path = xmalloc(baselen + 257);
                memcpy(path, base, baselen);

                while ((de = readdir(dir)) != NULL) {
                        char sha1[20];
                        struct stat st;
                        int namelen;

                        if (de->d_name[0] == '.')
                                continue;
                        namelen = strlen(de->d_name);
                        if (namelen > 255)
                                continue;
                        memcpy(path + baselen, de->d_name, namelen+1);
                        if (lstat(path, &st) < 0)
                                continue;
                        if (S_ISDIR(st.st_mode)) {
                                path[baselen + namelen] = '/';
                                path[baselen + namelen + 1] = 0;
                                write_head_info(path, nr, match);
                                continue;
                        }
                        if (read_ref(path, sha1) < 0)
                                continue;
                        if (nr && !path_match(path, nr, match))
                                continue;
                        show_ref(path, sha1);
                }
                free(path);
                closedir(dir);
        }
}

/*
 * This is all pretty stupid, but we use this packetized line
 * format to make a streaming format possible without ever
 * over-running the read buffers. That way we'll never read
 * into what might be the pack data (which should go to another
 * process entirely).
 *
 * The writing side could use stdio, but since the reading
 * side can't, we stay with pure read/write interfaces.
 */
static void safe_read(int fd, void *buffer, unsigned size)
{
        int n = 0;

        while (n < size) {
                int ret = read(0, buffer + n, size - n);
                if (ret < 0) {
                        if (errno == EINTR || errno == EAGAIN)
                                continue;
                        die("read error (%s)", strerror(errno));
                }
                if (!ret)
                        die("unexpected EOF");
                n += ret;
        }
}

static int safe_read_line(char *buffer, unsigned size)
{
        int n, len;

        safe_read(0, buffer, 4);

        len = 0;
        for (n = 0; n < 4; n++) {
                unsigned char c = buffer[n];
                len <<= 4;
                if (c >= '0' && c <= '9') {
                        len += c - '0';
                        continue;
                }
                if (c >= 'a' && c <= 'f') {
                        len += c - 'a' + 10;
                        continue;
                }
                if (c >= 'A' && c <= 'F') {
                        len += c - 'A' + 10;
                        continue;
                }
                die("protocol error: bad line length character");
        }
        if (!len)
                return 0;
        if (len < 4 || len >= size)
                die("protocol error: bad line length %d", len);
        safe_read(0, buffer + 4, len - 4);
        buffer[len] = 0;
        return len;
}

struct line {
        struct line *next;
        char data[0];
};

struct line *commands = NULL;

/*
 * This gets called after(if) we've successfully
 * unpacked the data payload.
 */
static void execute_commands(void)
{
        struct line *line = commands;

        while (line) {
                printf("%s", line->data);
                line = line->next;
        }
}

static void read_head_info(void)
{
        struct line **p = &commands;
        for (;;) {
                static char line[1000];
                int len = safe_read_line(line, sizeof(line));
                struct line *n;
                if (!len)
                        break;
                n = xmalloc(sizeof(struct line) + len);
                n->next = NULL;
                memcpy(n->data, line + 4, len - 3);
                *p = n;
                p = &n->next;
        }
}

static void unpack(void)
{
        pid_t pid = fork();

        if (pid < 0)
                die("unpack fork failed");
        if (!pid) {
                char *const envp[] = { "GIT_DIR=.", NULL };
                execle(unpacker, unpacker, NULL, envp);
                die("unpack execute failed");
        }

        for (;;) {
                int status, code;
                int retval = waitpid(pid, &status, 0);

                if (retval < 0) {
                        if (errno == EINTR)
                                continue;
                        die("waitpid failed (%s)", strerror(retval));
                }
                if (retval != pid)
                        die("waitpid is confused");
                if (WIFSIGNALED(status))
                        die("%s died of signal %d", unpacker, WTERMSIG(status));
                if (!WIFEXITED(status))
                        die("%s died out of really strange complications", unpacker);
                code = WEXITSTATUS(status);
                if (code)
                        die("%s exited with error code %d", unpacker, code);
                return;
        }
}

int main(int argc, char **argv)
{
        int i, nr_heads = 0;
        const char *dir = NULL;
        char **heads = NULL;

        argv++;
        for (i = 1; i < argc; i++) {
                const char *arg = *argv++;

                if (*arg == '-') {
                        if (!strncmp(arg, "--unpack=", 9)) {
                                unpacker = arg+9;
                                continue;
                        }
                        /* Do flag handling here */
                        usage(receive_pack_usage);
                }
                dir = arg;
                heads = argv;
                nr_heads = argc - i - 1;
                break;
        }
        if (!dir)
                usage(receive_pack_usage);

        /* chdir to the directory. If that fails, try appending ".git" */
        if (chdir(dir) < 0) {
                static char path[PATH_MAX];
                snprintf(path, sizeof(path), "%s.git", dir);
                if (chdir(path) < 0)
                        die("unable to cd to %s", dir);
        }

        /* If we have a ".git" directory, chdir to it */
        chdir(".git");

        if (access("objects", X_OK) < 0 || access("refs/heads", X_OK) < 0)
                die("%s doesn't appear to be a git directory", dir);
        write_head_info("refs/", nr_heads, heads);

        /* EOF */
        safe_write(1, "0000", 4);
        flush_safe(1);

        read_head_info();
        unpack();
        execute_commands();
        return 0;
}